Embodiments described herein generally relate to radio frequency (RF) receivers, and more particularly embodiments described herein relate to an RF peak detector circuit and an RF peak detector circuit method.
Unless otherwise indicated herein, the circuits and method described in the background section of this application are not prior art to the claims in this application and are not admitted to be prior art by inclusion in the background section.
RF receivers are used for receiving RF signals in numerous devices including personal mobile devices, such as mobile telephones, personal digital assistants (PDAs), computers, tablet computers, radios, global positioning system (GPS) receivers, and the like. RF receivers include an antenna configured to capture an RF signal and often include a tow-noise amplifier (LNA) for amplifying the RF signal. LNAs are configured to amplify relatively weak RF signals captured by an antenna. LNA are typically located close to an antenna to reduce losses in a circuit path from the antenna to the LNA. LNAs are often relatively high power devices that amplify an RF signal with relatively low noise and relatively little distortion introduced by the LNA.
Peak detectors are often included in an RF receiver at “critical” nodes of the RF receiver. Various critical nodes of an RF receiver include nodes that are after amplification stages, such as after LNAs. Peak detectors are often configured to operate in conjunction with an LNA and detect the power of the RF signal, or the like, output by the LNA. A peak detector may be configured to detect whether an LNA is saturated and/or operating non-linearly. A peak detector may be configured to operate in conjunction with an automatic gain controller that may receive a signal from a peak detector for lowering the gain of the LNA is operating in a saturation mode and/or is otherwise operating non-linearly. A peak detector operating in conjunction with an automatic gain controller is configured to provide that an LNA can operate with relatively high gain (e.g., maximum gain) and with relatively high sensitivity (e.g., maximum sensitivity).
FIG. 1 is a simplified schematic of a traditional RF receiver 1100 that includes an antenna 105, an LNA 110, a first peak detector 115, an automatic gain controller 120, a down-conversion mixer 125, a low-pass filter 130, a baseband amplifier 135, and a second peak detector 140. The antenna is configured to receive an RF signal and provide the RF signal to the LNA, which is configured to amplify the RF signal. The power of the amplified RF signal may be detected by the peak detector, which may provide a signal to the automatic gain controller for controlling the gain of the LNA to present the LNA from saturating. Subsequent to amplification by the LNA, the RF signal may be down converted to a baseband (e.g., 0-20 Mhz, 0-40 Mhz, etc.) by the down-conversion mixer and filtered by the filter to remove out-of-band signals (e.g., blocking signals). The filtered baseband signal may then be amplified by the baseband filter. The power of the amplified baseband signal may be detected by the second peak detector and provide a signal to the automatic gain controller for controlling the gain of the baseband amplifier. Subsequent processing of the RF signals may include digital to analog conversion and processing.
The node between the LNA and the down-conversion mixer is a critical node of the circuit operating at high frequency. The peak detector introduces a parasitic load on the LNA at the critical node and tends to degrade the operation of the LNA and hence degrade the operation of the RF receiver. One goal for RF receivers is to lower the parasitic load of the peak detector on the LNA. A peak detector may be designed for relatively low parasitic loading on an LNA at the expense of relatively high power consumption by the peak detector and relatively high circuit area on an IC.
Therefore, new circuit designs are needed for RF receivers for reducing the loading of peak detectors on amplification stages where the peak detectors are not relatively high power consumption and do not take up a relatively large area on an IC.